/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.hadoop.hbase;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer;
import org.apache.hadoop.hbase.zookeeper.MasterAddressTracker;
import org.apache.hadoop.hbase.zookeeper.ZKUtil;
import org.apache.hadoop.hbase.zookeeper.ZKWatcher;
import org.apache.hadoop.hbase.zookeeper.ZNodePaths;
import org.apache.yetus.audience.InterfaceAudience;
import org.apache.zookeeper.KeeperException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * <p>Contains a set of methods for the collaboration between the start/stop scripts and the
 * servers. It allows to delete immediately the znode when the master or the regions server crashes.
 * The region server / master writes a specific file when it starts / becomes main master. When they
 * end properly, they delete the file.</p>
 * <p>In the script, we check for the existence of these files when the program ends. If they still
 * exist we conclude that the server crashed, likely without deleting their znode. To have a faster
 * recovery we delete immediately the znode.</p>
 * <p>The strategy depends on the server type. For a region server we store the znode path in the
 * file, and use it to delete it. for a master, as the znode path constant whatever the server, we
 * check its content to make sure that the backup server is not now in charge.</p>
 */
@InterfaceAudience.Private
public final class ZNodeClearer {
    private static final Logger LOG = LoggerFactory.getLogger(ZNodeClearer.class);

    private ZNodeClearer() {
    }

    /**
     * Logs the errors without failing on exception.
     */
    public static void writeMyEphemeralNodeOnDisk(String fileContent) {
        String fileName = ZNodeClearer.getMyEphemeralNodeFileName();
        if(fileName == null) {
            LOG.warn("Environment variable HBASE_ZNODE_FILE not set; znodes will not be cleared " + "on crash by start scripts (Longer MTTR!)");
            return;
        }

        FileWriter fstream;
        try {
            fstream = new FileWriter(fileName);
        } catch(IOException e) {
            LOG.warn("Can't write znode file " + fileName, e);
            return;
        }

        BufferedWriter out = new BufferedWriter(fstream);

        try {
            try {

                /********
                 * TODO_MA 马中华 https://blog.csdn.net/zhongqi2513
                 *   注释：
                 */
                out.write(fileContent + "\n");
            } finally {
                try {
                    out.close();
                } finally {
                    fstream.close();
                }
            }
        } catch(IOException e) {
            LOG.warn("Can't write znode file " + fileName, e);
        }
    }

    /**
     * read the content of znode file, expects a single line.
     */
    public static String readMyEphemeralNodeOnDisk() throws IOException {
        String fileName = getMyEphemeralNodeFileName();
        if(fileName == null) {
            throw new FileNotFoundException("No filename; set environment variable HBASE_ZNODE_FILE");
        }
        FileReader znodeFile = new FileReader(fileName);
        BufferedReader br = null;
        try {
            br = new BufferedReader(znodeFile);
            String file_content = br.readLine();
            return file_content;
        } finally {
            if(br != null)
                br.close();
        }
    }

    /**
     * Get the name of the file used to store the znode contents
     */
    public static String getMyEphemeralNodeFileName() {
        return System.getenv().get("HBASE_ZNODE_FILE");
    }

    /**
     * delete the znode file
     */
    public static void deleteMyEphemeralNodeOnDisk() {
        String fileName = getMyEphemeralNodeFileName();

        if(fileName != null) {
            new File(fileName).delete();
        }
    }

    /**
     * See HBASE-14861. We are extracting master ServerName from rsZnodePath
     * example: "/hbase/rs/server.example.com,16020,1448266496481"
     *
     * @param rsZnodePath from HBASE_ZNODE_FILE
     * @return String representation of ServerName or null if fails
     */

    public static String parseMasterServerName(String rsZnodePath) {
        String masterServerName = null;
        try {
            String[] rsZnodeParts = rsZnodePath.split("/");
            masterServerName = rsZnodeParts[rsZnodeParts.length - 1];
        } catch(IndexOutOfBoundsException e) {
            LOG.warn("String " + rsZnodePath + " has wrong format", e);
        }
        return masterServerName;
    }

    /**
     * @return true if cluster is configured with master-rs collocation
     */
    private static boolean tablesOnMaster(Configuration conf) {
        boolean tablesOnMaster = true;
        String confValue = conf.get(BaseLoadBalancer.TABLES_ON_MASTER);
        if(confValue != null && confValue.equalsIgnoreCase("none")) {
            tablesOnMaster = false;
        }
        return tablesOnMaster;
    }

    /**
     * Delete the master znode if its content (ServerName string) is the same
     * as the one in the znode file. (env: HBASE_ZNODE_FILE). I case of master-rs
     * colloaction we extract ServerName string from rsZnode path.(HBASE-14861)
     *
     * @return true on successful deletion, false otherwise.
     */
    public static boolean clear(Configuration conf) {
        Configuration tempConf = new Configuration(conf);
        tempConf.setInt("zookeeper.recovery.retry", 0);

        ZKWatcher zkw;
        try {
            zkw = new ZKWatcher(tempConf, "clean znode for master", new Abortable() {
                @Override
                public void abort(String why, Throwable e) {
                }

                @Override
                public boolean isAborted() {
                    return false;
                }
            });
        } catch(IOException e) {
            LOG.warn("Can't connect to zookeeper to read the master znode", e);
            return false;
        }

        String znodeFileContent;
        try {
            znodeFileContent = ZNodeClearer.readMyEphemeralNodeOnDisk();
            if(ZNodeClearer.tablesOnMaster(conf)) {
                // In case of master crash also remove rsZnode since master is also regionserver
                ZKUtil.deleteNodeFailSilent(zkw, ZNodePaths.joinZNode(zkw.getZNodePaths().rsZNode, znodeFileContent));
                return MasterAddressTracker.deleteIfEquals(zkw, ZNodeClearer.parseMasterServerName(znodeFileContent));
            } else {
                return MasterAddressTracker.deleteIfEquals(zkw, znodeFileContent);
            }
        } catch(FileNotFoundException fnfe) {
            // If no file, just keep going -- return success.
            LOG.warn("Can't find the znode file; presume non-fatal", fnfe);
            return true;
        } catch(IOException e) {
            LOG.warn("Can't read the content of the znode file", e);
            return false;
        } catch(KeeperException e) {
            LOG.warn("ZooKeeper exception deleting znode", e);
            return false;
        } finally {
            zkw.close();
        }
    }
}
